1. Field of the Invention
This invention relates to a machine method of adjusting circuits, and more particularly, to a machine method of controlling the adjustment of adjustable circuit components wherein target values are calculated for components to be adjusted.
2. DESCRIPTION OF THE PRIOR ART
Methods of machine adjustment of adjustable components in electronic circuits are well known. For example, an article by James Dupcak and Roger H. DeGroot entitled "The Manufacture of Thin-Film Active Filters" on pp. 18-25 of The Western Electric Engineer dated July, 1974 describes how components in a thin-film filter circuit can be machine-adjusted to tune the filter circuit.
In the method described in the above article, non-adjustable components comprising capacitors are measured, then the measured values are used by a digital computer for calculating target values for adjustable components comprising resistors. The adjustable resistors are then trimmed to their target values, within narrow tolerance limits, using an anodizing process. The resulting parameters of the circuit being adjusted will be within tolerance limits if all the components are trimmed within their tolerance limits.
An adjustable component, such as a resistor, can be adjusted to be within relatively wider tolerance limits in a shorter time than it can be adjusted to be within relatively narrower tolerance limits. If a circuit such as that in the above article is to have its parameters typically within specified limits, and if the target values of its adjustable components are all calculated before any of the adjustable components are trimmed, the adjustable components must be trimmed to quite narrow tolerances, such as 0.3%. In contrast, if the measured value of an already-trimmed first adjustable component could be fed back into the calculations before a second adjustable component were trimmed, the target value of the second component could be chosen to compensate for error in the first component, and so on, and all the adjustments could be made to wider tolerances, for example, 0.6%. Heretofore, such a process has not been practical because of the complicated calculations necessary to incorporate errors of prior adjustments into target values for subsequent adjustments. Thus, it is a difficulty with prior-art component adjusting methods that the precision adjustments necessary require substantial time.
An adjustment method wherein target values for passive circuit components are calculated from theoretical circuit relationships and the components are adjusted without actual operation of the circuit is called deterministic adjustment. Typically, deterministic adjustment is performed on an incomplete circuit before active elements are assembled into the circuit, and when many passive components may be so far from their final values that proper operation of the circuit would not be possible even if active components were present.
Another adjustment method, functional adjustment, involves adjustment of components in a completed, operating circuit to correct operating parameters of the circuit. For example, a filter circuit can be functionally adjusted by measuring gain or phase shift at specific frequencies and adjusting components to bring the gain or phase shift within specifications. Functional adjustment can also compensate for variations in active components.
It is often convenient to perform both deterministic adjustment and functional adjustment on a circuit: a preliminary deterministic adjustment without active components in the circuit to bring passive component values into tolerance, followed by a functional adjustment after active components have been added.
A difficulty with both deterministic and functional computer-controlled component adjusting systems is setting up such a system for different configurations of adjustable circuits. In the past, it has been necessary to program the control computer in such a system to solve equations derived from the configuration of the circuit being adjusted to determine target values for the adjustable components. For example, see Section VII of the article entitled "RC Active Filters for the D3 Channel Bank," by R. A. Friedenson, R. W. Daniels, R. J. Dow, and P. H. McDonald in the March 1975 issue of The Bell System Technical Journal. Encoding such equations requires the services of skilled programmers, and solving such equations to determine target values is inefficient and time consuming in the small process-control computers typically used to control circuit adjusting systems.
It is desirable, therefore, to devise both deterministic and functional methods of adjusting circuit components that will be faster than prior art systems, that will enable adjustments to be made with wider tolerances on individual components, and that can be easily implemented on a small process-control computer for different circuit configurations.